Add Hakyll site generator and assets

Add site executable and Haskell modules (site.hs, ChaoDoc.hs,
SideNoteHTML.hs, Pangu.hs) to handle Pandoc/Hakyll compilation,
theorem/sidenote processing and CJK spacing. Add CSS, font files,
favicon, templates, Makefile, and a CSL bibliographic style. Update
.gitignore to ignore build artifacts.

prompts/ask-question.md

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+You will be solving an extremely challenging mathematics question. The answer may not be known to anyone.
+
+Feel free to think out loud as much as you want. You also have a MacOS environment and some tools available to help you.
+
+Tips for solving:
+* **Try your hardest to answer it.** Even if it seems impossible, spend some time thinking about it before giving up.
+* **Create a plan.** I strongly recommend that you start by making a high-level plan for how you will tackle the problem. Revise your plan along the way if necessary.
+
+Ideas to try if you get stuck:
+* Think about other, similar problems.
+* Try first solving a simpler version of the problem.
+* Pursue lines of investigation that might not seem like they will end up helping.
+* Brainstorm new approaches and try each of them.
+
+Tips for writing: in markdown use `#` for sections and `##` for subsections. Write title in yaml section.
+